Heat treatment process improving the mechanical properties of aluminiummagnesium-silicon alloys



June 2, 1964 J. c. HORNUS 3 135 633 HEAT TREATMENT PROCESS IMPROVING THEMECHANICAL PRorERTIEs OF ALUMINIUM-MAGNESIUM-SILICON ALLOYS Flled Sept.2, 1960 4 Sheets-Sheet 1 Fig. 2

- 4 fifihours BREAKING LOAD kq/mm 10 50min.

EFFECTS OF TEMPERATLRE AND TIME OF DELAY BETWEEN QUENCHING AND AGINGTIME OF DELAY BETWEEN QUENCHING AND AGING JEAN-CLAUDEJIORNUS ATTORNEYSJune 2 1964 J. c. HORNUS 3 135 6 HEAT TREATMENT PROCESS IMPROVING THEMECHANICAL PRO1 ERTI ES OF ALUMINIUM-MAGNESIUM-SILICON ALLOYS 4Sheets-Sheet 2 Filed Sept. 2, 1960 02:3 024 0250225 zmwgkmm 03w 3 :81 M3 5 v 2 3 m v INVENTOR JEAN-CLAUDES HORNUS BY 4494;?

ATTOR'NEYS J. C. HORNUS June 2, 1964 HEAT TREATMENT PROCESS IMPROVINGTHE MECHANICAL PROPERTIES OF ALUMINIUM-MAGNESIUNFSILICON ALLOYS 4Sheets-Sheet 3 Filed Sept. 2. 1960 02-04 024 wziozmnc ZmwEmm mfiw '9,INVENTOR JEAN-C LAUDE HORNUS BY M 7 ATTORNEYS J1me 1954 J. c. HORNUS3,135,633

HEAT TREATMENT PROCESS IMPROVING THE MECHANICAL PROPERTIES OFALUMINIUMMAGNESIUMSILICON ALLOYS Filed Sept. 2-. 1960 4 Sheets-Sheet 4INVENTOR JEAN-CLAUDE HORNUS ATTORNEYS United States Patent 3,135,633HEAT TREATMENT PROCESS IM'PRQVING THE MECHANICAL PROPERTIES OFALUMINIUM- MAGNESHJM=SILICON ALLOYS Jean Ciaude Hornus,Neniily-sur-Seine, France, assignor to Compagnie Generaie du Duralurninet du Cuivre, Paris, lh'ance, a French corporation Filed Sept. 2, 1960,Ser. No. 53,809 Claims priority, application France Sept. 8, 1959Claims. (Cl. 148-469) below the use of a forced convection laboratoryfurnace for artificial aging instead of a salt-bath furnace led to alowering of the mechanical properties E and R by about 3 kg./mm.although the necessary rise in temperature in the air furnace only tookone hour, that is, much less than is used in industrial artificial agingof fagots.

TABLE Effect of Rate of Healing to Annealing Temperature Upon theMechanical Properties of A-SG Type Alloys Eo,z(kg./ R(kg./ Amt mm] mm.Percent Soaked 20 min. at 550 C. and

water quenched Immediate aging in a salt bath for 6 hours at 175 C.(heating-up practically instantaneous) 34. 2 39.1 18. 8 Immediate agingin an air furnace:

Length of heating-up, 1 hr Hglfi at temperature (175 0.) 31 3 36. 1 l9.7

The heat treatment of 20 min. at 550 C. is a solution treatment.

In practice, aluminium-magnesium-silicon alloys are obtained withconsiderably poorer mechanical properties (often 7 to 8 kg./mm. poorer)than the mechanical properties they could reach, for the following tworeasons.

Firstly, handling difficulties and the necessity for finishing thesurface before artificial aging prevent starting the aging immediatelyafter quenching.

Secondly, by reason of the harmful consequences, to the surface of thesheets, when aging in a salt or an oil bath, it is customary to carryout the aging in air furnaces. When aging fagots, heating is ofnecessity slow.

On the other hand, the problem of full aging with rapid heating cannotbe solved by using an air circulating continuous furnace because agingis a slow process which cannot be cut short, even by raising thetemperature, Without greatly reducing the mechanical propertiesobtained. Now, a continuous air circulating furnace with passages, if itgives rapid heating only allows of relatively short treatments.

To remedy the inconveniences of an inevitable delay between quenchingand artificial aging, it is proposed to subject the alloy, immediatelyafter quenching, to a short preliminary aging, followed by a final fullaging after a delay of a few days.

But application of such a process has run up against many obstacles upto the present. It is particularly difficult to make handlingsufiiciently rapid and to carry out a perfect synchronizing ofoperations. Moreover, if the furnace used to obtain the high speed ofheating up which is necessary is a salt-bath or oil-bath furnace, thisresults in the inconveniences already mentioned above.

The aim of the present invention is to carry out a pro-aging orstabilizing treatment of aluminum-magnesium-silicon alloys industriallyin order to improve their mechanical properties by amounts up to 25% Theinvention consists in a heat treatment process for Wrought products ofaluminium-magnesium-silicon alloys, in which the wrought products aremoved along continuously through a first furnace to put an additiveelement or elements into solid solution in the base element, thenthrough a quenching chamber and into a second furnace to be subjected toa stabilizing preliminary aging, at least the second furnace beingheated by forced hot air circulation, and the time interval betweenquenching and reaching preliminary aging temperature being less than tenminutes, the stabilized wrought products being subjected to a final fullaging at a later time. Conveniently the first furnace is also heated byforced hot air circulation.

The quenching may be by means of forced air cooling, water sprays ormist sprays.

The straightening or otherwise finishing of the wrought product isconveniently incorporated after the preliminary aging and before thefinal full aging.

The invention further consists in apparatus for carrying into practice aheat treatment process in which a conveyor bearing the wrought productsto be treated is arranged to pass in series through a first furnace toput the additive elements in solution in the base element, a quenchingchamber and a second furnace to subject the articles to a stabilizingpreliminary aging, at least the second furnace being heated by forcedhot air circulation. Means may be provided for heating both furnaceswith forced hot air circulation and for quenching with forced aircooling, water spraying or mist spraying, if necessary.

Furthermore, a device for straightening or otherwise shaping of thewrought products may be provided after the second furnace.

Thus, all the steps needed, i.e., the solution treatment, the quenchingproper, preliminary aging and straightening if performed are effectedcontinuously, and the time interval between quenching and preliminaryaging is re-. duced to less than ten minutes, even for low speeds ofmovement of the order of 1 meter per minute, which allows the alloy tobe given the highest mechanical properties it can possibly get.Moreover, the preliminary aging or stabilizing treatment, as it iscarried out in an air furnace, involves no cleaning, degreasing, orscouring which particularly allows, as already remarked upon, in-

tegrating the shaping or straightening of the product into a continuousseries of operations.

The final aging may be carried out any time in the week following thestabilising preliminary aging.

The plant needed for this process is not unduly burdensome to construct,for the three operations needing heat, namely; solution treatment,quenching, and preliminary aging or pre-annealing may be carried outmerely by blowing in air which has the correct temperature for therelevant step, i.e., of the order of 550 C. for the first step, about 20C. for the second and between C. and 250 C. for the third.

Actually, use of water for quenching hardly changes the economicconditions, i.e., the process is still economically workable.

It is felt that the process according to the invention is the only onewhich allows the solution treatment, the quenching and the stabilizingpreliminary aging to be carried out industrially in a short time, andresults in good mechanical properties for aluminium-magnesiumsiliconalloys after final aging. The quenching and stabilizing preliminaryaging may take place within five minutes of one another.

Carrying out these same steps by different methods (salt-bath, orair-furnace or oil-bath for preliminary aging or stabilization)militates against a short treatment because of accessory steps(intermediate cleaning or degreasing), or of handling.

The invention may be further described with reference to theaccompanying drawings which are illustrative and are not intended to belimitative in any way.

FIGURE 1 shows, for a non-stabilized specimen, time of delay betweenquenching and full aging, plotted against temperature maintained duringthat delay, with the solid lines joining points where conditions givethe same values for the yield strength.

FIGURE 2 is a similar graph, but in which the solid lines join pointswhere conditions give the same values for the tensile strength.

FIGURES 3 and 4 show the eflect of stabilizing treatments as a functionof their duration and of the gap between quenching and stabilization.

FIGURE 5 is a somewhat diagrammatic cross-section through an apparatusfor carrying out the heat treatment process of the invention.

By way of example, FIGURES 1 and 2 of the accompanying drawing areprovided to summarize the results of various experiments on plates of athickness of 12/10 mm., made of an alloy known by the abbreviation ofA$G.

In FIGURES 1 and 2, time of delay is shown on the abscissa from zero to7 days, and temperatures of delay upon the ordinates. As may be seenfrom the curves, a delay of about one day between quenching andannealing lowers the yield strength to less than 26 kg./ mm. (FEGURE l)and the tensile strength to less than 32 kg./mrn. (FIGURE 2), althoughthe same alloy, if it has undergone an artificial aging immediatelyafter quenching has a yield strength of 35 to 36 kg./mm. (FIGURE 1) anda tensile strength of 39 to 40 kg./rnm. (FIGURE 2).

The FIGURES 3 and 4 were obtained with sheets 1.3 mm. thick; thesolution treatment lasted 30 minutes at 540 C. and artificial aginglasted hours at 160 C.; the stabilization treatment by preliminary agingtook place at 140 C.

As abscissa, lengths of time are shown from zero to 14 days betweenquenching and annealing or artificial aging. On the left hand ordinate,the values of the yield strength, and on the right, the values oftensile strength, are in dicated.

The curves drawn in solid lines are those obtained withoutstabilization; those drawn in dashed lines correspond to stabilizationtaking place 3 minutes after quenching; for those in dash-dot linesstabilization took place 7 minutes after quenching; for those drawn indash-double dot lines stabilization took place minutes after quenching.Finally, for those drawn in dotted lines stabilization took place 2hours after quenching.

In passing from FIGURE 3 to FIGURE 4 and from left to right in eachfigure, the curves below give the values of the yield strength and thoseabove give the values of the tensile strength; the duration of thestabilization treatment is arranged in the order of the curves and wassuccessively 2 minutes, 4 minutes, 8 minutes, 16 minutes, 32 minutes and64 minutes.

Another advantage of a treatment of some minutes at a temperaturebetween 100 C. and 250 C. is that it does not harden the alloy to theextent of hindering the straightening or shaping of the product, shouldthis be done as usual prior to the final full aging.

In FIGURE 5, a high warm-up speed furnace It, in which the products maybe kept for from 2 to minutes at temperatures between 450 C. and 600 C.is provided for the solution treatment. Following this, a

quenching chamber 2 where cooling is effected by known means, such aswater, air, or some combination of both, is placed.

A preliminary aging, forced connection furnace 3 comes next in which theproducts are kept for from 1 to 10 minutes in circulating air attemperatures between C. and 250 C.

The plant is fed with products by a single conveyor 4- passingsuccessively into the two furnaces and which provides perfectsynchronization of the plant. An entry platform 5 and leaving platform 6allows respectively for feeding, and recovering treated products from,the conveyor.

The interval between quenching and preliminary aging is automaticallylimited to a length of time under 5 minutes.

For sheets, the plant may be completed at the end of the pre-annealingfurnace with some device to straighten or shape the sheets as they leavethe conveyor 4.

Various modifications may be made within the scope of the invention.

I claim:

1. A continuous heat treatment process for improving the physicalproperties of alloys of aluminium, magnesium and silicon, comprisingsubjecting an aluminium-magnesiurn-silicon alloy to solution heattreatment at a temperature of between approximately 450 to 600 C.,quenching the alloy to approximately room temperature, reheating thealloy to a temperature of from approximately 100 to 250 C. topreliminarily age the alloy within a few minutes after quenching, andsubsequently again heating the alloy in order to finally age the alloy.

2. A continuous heat treatment process for improving the physicalproperties of alloys of aluminium, magnesium and silicon capable ofspontaneous aging, comprising subjecting an aluminium-magnesium-siliconalloy to solution heat treatment at a temperature of betweenapproximately 450 and 600 C., quenching the alloy to approximately roomtemperature, briefly reheating the alloy to a temperature of fromapproximately 100 to 250 C. by hot air heating to preliminarily age thealloy within a few minutes after quenching, cooling the alloy after ashort period of time, and subsequently again heating the alloy in orderto finally age the alloy.

3. A continuous heat treatment process for improving the physicalproperties of aluminium containing alloys which spontaneously age withtime, comprising subjecting such an alloy to solution heat treatment ata temperature between about 450600 C. cooling the alloy to approximatelyroom temperature to quench the same, reheating the alloy within a fewminutes after quenching to a temperature substantially lower than thesolution heat treatment temperature for a period of approximately 10minutes to preliminarily age the alloy, and cooling and storing thealloy to await a subsequent final aging.

4. An essentially continuous heat treatment process for improving thephysical characteristics of an aluminiummagnesium, silicon alloy,comprising the steps of substantially continuously and successivelypassing said alloy through a first hot air furnace zone, solution heattreating the alloy in said first furnace zone at a temperature ofapproximately 450 and 600 C., passing the alloy into a cooling zone toquench the same to approximately room temperature, passing the quenchedalloy into a second hot air furnace zone, preliminarily aging the alloyin said second hot air furnace zone by heating with circulating hot airto a temperature above approximately 100 C. and substantially below saidfirst-mentioned temperature, and removing the preliminarily aged alloyfrom said second hot air furnace zone for storage prior to final agingthereof.

5. An essentially continuous heat treatment process for improving thephysical characteristics of an aluminiummagesium-silicon alloy,comprising the steps of substantially continuously and successivelypassing said alloy through a first furnace zone, solution heat treatingthe alloy therein at a temperature of between approximately 450 and 600C., passing the alloy into a cooling zone to quench the same toapproximately room temperature, passing the quenched alloy into a secondfurnace zone within several minutes after quenching, preliminarily agingthe alloy in said second furnace zone by reheating the alloy for a shortperiod of time to a temperature of between approximately 100 and 250 C.,and removing the preliminarily aged alloy from said second furnace zonefor storage prior to final aging thereof.

6. A substantially continuous process for treatingaluminium-magnesium-silicon alloys which age spontaneously with time atroom temperatures, comprising the steps of solution heat treating analuminium-magnesium-silicon alloy at a temperature between 450600 C.,quenching the resultant product to approximately room temperature, andsubstantially immediately thereafter preliminarily aging the quenchedproduct by heating to temperatures in the order of 100 to 250 C. wherebythe physical properties of the alloy remain substantially unaffected bythe passage of time while awaiting final aging treatment.

7. A process as defined in claim 6, wherein forced air is used to quenchthe alloy.

8. A process as defined in claim 6, wherein the preliminary aging iscarried out in a forced air furnace.

9. A process as defined in claim 6, further comprising shaping the alloyto a desired configuration after the preliminary aging thereof.

10. An essentially continuous process for improving the physicalcharacteristics of an aluminium-magnesium-silicon alloy which agesspontaneously with time at room temperatures, comprising the steps ofsubstantially continuously and successively passing said alloy through afirst heating zone, solution heat treating the alloy therein at atemperature between 450-600 C. for a period of about 2-20 minutes,passing the alloy into a cooling zone to quench the same toapproximately room temperature, passing the quenched alloy into a secondheating zone within several minutes after quenching, preliminarily agingthe alloy in said second heating zone by reheating the alloy between-250 C. for about ten minutes by contact with forced heated air, andremoving the preliminarily aged alloy from said second heating zone forstorage prior to final aging thereof.

References Cited in the file of this patent UNITED STATES PATENTS NockJune 15, 1937 OTHER REFERENCES

1. A CONTINUOUS HEAT TREATMENT PROCESS FOR IMPROVING THE PHYSICALPROPERTIES OF ALLOYS OF ALUMINIUM, MAGNESIUM AND SILICON, COMPRISINGSUBJECTING AN ALUMINIUM-MAGNESIUM-SILICON ALLOY TO SOLUTION HEATTREATMENT AT A TEMPERATURE OF BETWEEN APPROXIMATELY 450* TO 600*C.,QUENCHING THE ALLOY TO APPROXIMATELY ROOM TEMPERTURE, REHEATING THEALLOY TO A TEMPERATURE OF FROM APPROXIMATELY 100 TO 250*C. TOPRELIMINARILY AGE THE ALLOY WITHIN A FEW MINUTES AFTER QUENCHING, ANDSUBSEQUENTLY AGAIND HEATING THE ALLOY IN ORDER TO FINALLY AGE THE ALLOY.